Maximum Download Speed

Answered Question
Oct 28th, 2008

Hi Everyone,

I have connected two pc with giga nic to a giga bit switch, and i am trying to transfer a file from one system to another.what should be the maximum file transfer rate that i can expect. is it going to be the trasfered in giga range or some what below..

Thanks

Joe

I have this problem too.
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Correct Answer by Joseph W. Doherty about 8 years 2 months ago

Many factors will determine transfer speed.

For starters, although the bit rate on your wire is gig, some of those bits are required for "packaging" your actual data. Assuming the transfer is running on top of TCP and assuming your using "normal" Ethernet which allows 1500 byte packets, you'll lose about 3 to 4%. The overhead decreases if jumbo Ethernet is supported, and rises (much) as you move to smaller and smaller packets.

The 3 or 4% is a minor loss, but much more can be loss due to client application protocols (e.g. Windows original CIFS protocol is often slower than FTP), client stack implementations (Windows XP can be much slower than Windows Vista), the quality of the host NICs and their drivers, and also the performance of your gig switch.

At gig speeds, you can also run into issues that the end hosts can not feed or receive at full speed due to disk architecture limitations (PATA, vs. SATA, vs. SCSI; drive specifications; single drive vs. RAID; etc.)

If you can hit about 90% of line rate, you're doing well. If you can't get above 70%, you might need to run down which of the prior issues might be causing the slowness.

Do remember, lots of clients reports speeds in bytes per second, but network speeds are reported in bits second.

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Correct Answer
Joseph W. Doherty Tue, 10/28/2008 - 06:40

Many factors will determine transfer speed.

For starters, although the bit rate on your wire is gig, some of those bits are required for "packaging" your actual data. Assuming the transfer is running on top of TCP and assuming your using "normal" Ethernet which allows 1500 byte packets, you'll lose about 3 to 4%. The overhead decreases if jumbo Ethernet is supported, and rises (much) as you move to smaller and smaller packets.

The 3 or 4% is a minor loss, but much more can be loss due to client application protocols (e.g. Windows original CIFS protocol is often slower than FTP), client stack implementations (Windows XP can be much slower than Windows Vista), the quality of the host NICs and their drivers, and also the performance of your gig switch.

At gig speeds, you can also run into issues that the end hosts can not feed or receive at full speed due to disk architecture limitations (PATA, vs. SATA, vs. SCSI; drive specifications; single drive vs. RAID; etc.)

If you can hit about 90% of line rate, you're doing well. If you can't get above 70%, you might need to run down which of the prior issues might be causing the slowness.

Do remember, lots of clients reports speeds in bytes per second, but network speeds are reported in bits second.

sr2623235 Tue, 10/28/2008 - 23:51

Thanks for your great reply..i really appreciate it.surely i will rate this.

Joseph W. Doherty Wed, 10/29/2008 - 05:21

Thank you for the comments, but forgot to add to my original post, you might find using a traffic generator useful for checking network performance. Often simple ones can be found for free. Such host to host traffic tests bypass many of the issues that can impact network data transfer performance. (I.e. many of these test applications should be able to hit full wire rate across your network.)

sr2623235 Wed, 10/29/2008 - 12:41

that was great...i really liked that...i downloaded some and i am going to try now...thanks for you great help...

itdsmartnet Sun, 11/02/2008 - 21:33

hi,

please let me know the name of some application to test the link.

Thanks

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